New Cartridge: 458 dropbear

Inspired by the recent introduction of the 45 Raptor, an Australian shooter using the screen name of Quan-Time worked up another bigbore round based on the 308 Winchester case. The new round is called the 458 dropbear.

Quan-Time details the cartridge and the process he used to develop it at the Overclockers Australia forum here. If you have an interest in how one develops a new load, it is definitely worth the read.

The initial load tested used a .458 caliber, 350 grain Woodleigh RN bullet over 42.5 grains of ADI 2208 powder. (Note: According to ADI, 2208 is approximately equivalent to Hodgdon Varget and IMR 4064. Read this for additional information.) This load produced about 1,600 fps without a crimp and an estimated chamber pressure of 24,500 psi – well under the maximum established for the 308 Winchester. With additional development, this cartridge should be well above 2,000 fps.

Dillon Precision used to brag on the fact that their dies would create a Coke Bottle effect in the loaded round. Whatever case taper is there will be fire-formed out upon the first firing.

It strikes me that the .450 Bushmaster would be ideal for reworking to 0.458″ projectiles. Then you could trim down a set of .45-70 dies.

guest

What is really needed is a very heavy bullet equipped wildcat of a 308 that can be an adequate answer to 9×39 and manufactured from 308 brass, instead of the weak .300 blackout. I am thinking here of something like 300gn .338 lapmag bullets or similar, something ridiculously heavy and VLD, to make a very good sub cartridge. This however is yet another hunting wildcat (oh lord, not another one! Do we really need 100000000 of them?) that has an abnormal shape to boot, which probably will not fit well or cause jams in 7.62 mags

The sectioned chamber shown was just to prove that the round could headspace on the case mouth. It does not represent the final dimensions of an actual chamber

patrickiv

I think Mystick is referring to the first photo, wherein the top half of the case is larger than the bottom half. If this was inserted into a complete chamber, the rear half wouldn’t be in contact with the chamber wall before firing.

There is a fair amount of case expansion with any factory cartridge/factory chamber combination. There is a reason why accuracy-minded shooters recommend only neck-sizing the brass and segregating the cases to a specific rifle.

Chambers in military surplus rifles can be even worse in this regard.

Mystick

That was indeed the basis for my assertion. “In battery” meaning round fully in the chamber… you couldn’t insert it into the chamber and have full contact with all of the brass since the BACK of the brass is smaller than the front. That’s why rounds are necked down, and not up, as the the case here.

I just don’t see it working without a split chamber, and then – why have a split chamber?

Base the round off of something larger than a .308 cartridge if you are going to exceed its maximum diameter with the projectile.

The 6.5x55mm Swede might be better in this regard for the parent case.

Steve Truffer

You ever see a piece of 9×19 brass converted to 9×18, but before initial fireforming? Its fine, brass is MUCH thicker at the web than the neck.

opie

so how will it extract with the top of the case wider than the base? seems like another solution to a problem that does not exist..i just see no point in this cartridge, but thats just me.

Dchil

Not a problem for us aussies, We don’t run them through semi autos (99% of the time) so we can take the time to actually cycle the bolt ourselves and make sure the cases actually come out.

Also the case is probably wider at the top because it hasn’t been fire formed but is just a 308 case stretched a bit to allow the 458 bullet so it isn;t exactly the same size.

Tothe

Why not step up to a .338 Win Mag case for this kind of load anyway?

billyoblivion

Dood, seriously, have you ever SEEN a drop bear in the wild?

Extraction doesn’t matter. If you see it before it sees you you get ONE shot and it’s gone. If you don’t see it first, well, you won’t get that shot.

smartacus

i’m gonna start building a 458 dropROFLbear after i finish my .17BMG

smartacus

oh hahaha yer so funny we forgot to laugh.

Blastattack

Did you just insult yourself? That’s gold mate.

Giolli Joker

…or that’s bipolar…
😀

Beaumont

Consider me a skeptic. Harry Sanford tried something similar decades ago, and found that the largest slug one can stuff into an opened-up .308 case, without bulging, is .429 diameter, usually thought of as .44 cal. He called his round the .44 AMP, and it worked reasonably well. Even if the brass fireforms in the chamber, which I doubt, the case mouth may well be too thin to headspace properly. If the inventor is reading this, I say, prove me wrong.

Part of the issue with the .44 AMP is that the case walls get thicker the lower you go on the parent case. I could see a larger caliber being feasible with the half-inch difference in case length. But you are correct that the case mouth is going to be very thin.

Beaumont

Now that I think of it, I read an article by one of the outdoors-magazine gunwriters (don’t remember his name) about his attempts to build a .450 wildcat on a .30-06 case, & encountering that very issue. Sadly, I have no idea where I read that.

There’s always salties, those can get up to around 20′ long although I don’t know that you’re allowed to hunt crocs or that you’d really want to. Then there’s the feral pig population, I believe those are fair game and a round that can take out a bear should be more than enough to take out a wild pig.

I have 2 Bxs of unfired 762X51 Rimmed if we worked hard I bet we could reproduce 45-70 velocities in a Ruger No1! ROLF

BeGe1

Can someone please tell me why one would EVER neck UP a .308 to larger than the main body diameter, when the parent case to .308 is the much longer .30-06 which could be cut to .308 length and not have a shoulder in the first place?